Coatings in kitchens and bathrooms must be highly resistant to liquids (both water and oils) and withstand heat and humidity. Conventional aqueous UV coating compositions for use in wood finishing are often processed on a spray painting machine. After conditioning, the coated surface is usually sanded and polished. By the sanding and polishing process, a part of the lacquer is normally removed and the surface is then re-polished to a high gloss finish by using waxes and buffing units. There is some risk that the paint layer gets damaged by the polishing process, especially in the areas of edges and corners, if the coating layer is not thick enough. However, the amount of lacquer which can be applied in one step is normally limited to an amount of 130 g/m2 or less. This is due to the fact that with conventional aqueous UV coating compositions higher amounts or higher thicknesses are often associated with inadequate curing and/or blistering/micro-foam formation resulting from air remaining in the paint layer at high film thicknesses.
In order to have enough paint material on the edges and corners which remains undamaged in the course of the final polishing process and which avoids micro-foam formation at the paint surface, it is thus normally required to apply at least two lacquer layers, each e.g. in an amount of about 100-130 g/m2, which have to be applied in a multi-step process. After application of a first coating layer the surface is usually subjected to a drying phase of about 45 minutes followed by UV curing. Before applying a second layer the surface is normally sanded. Then a second layer is sprayed on top of the first layer, again followed by a drying phase and UV curing. Such a multi-step process is both time-consuming and cost-intensive.
It would be desirable to have a UV coating composition where less process steps are required, i.e. where e.g. one coating step and one sanding operation could be saved. In other words, there is a need for a UV coating composition which allows for an application of a high enough film thickness (coating in an amount of about 180-250 g/m2) in one single coating step, while highly reducing or avoiding inadequate curing and/or micro-foam formation.